The invention concerns a cup tappet for a valve train of an internal combustion engine, said cup tappet comprising a hollow cylindrical skirt whose one end is connected to a bottom for making contact with a cam.
A generic cup tappet of the pre-cited type known from the document DE 41 15 668 A1 comprises a hydraulic clearance compensation element. A drawback of this tappet is its relatively solid configuration, particularly in the region of the bottom. Due to this, the oscillating mass of the valve train is unnecessarily increased so that the amount of work that has to be performed in the valve train is too large.
It is an object of the invention to provide an improved cup tappet of the pre-cited type that is optimized with regard to its weight.
This and other objects and advantages of the invention will become obvious from the following detailed description.
The invention achieves the above objects by the fact that a height of the skirt is clearly smaller than an overall height of the cup tappet, and the bottom rises in a roof-like taper from the end of the skirt.
According to a particularly advantageous feature of the invention, the bottom has a rectangular shape extending in a direction of outward travel of a cam-contacting surface.
Due to this roof-like xe2x80x9crisexe2x80x9d of the bottom, the rigidity in this region is enhanced. This, in its turn, permits a significant reduction of the thickness of the bottom to about 1.2 mm. At the same time, as a result of the simultaneous reduction of the height of the skirt and the overall surface of the bottom, the total surface requiring fine machining is small. This has an advantageous effect on the cost and work of fabrication.
Although it is particularly proposed that the bottom have a rectangular shape, so that two parallel sides extend from the end of the skirt toward the bottom, it is possible, if required, to realize a frustoconical configuration with a circular bottom. In this case, however, only a relatively small contact surface for the cam is formed on the bottom.
According to a further proposition of the invention, the parallel sides extending toward the bottom can have a concave configuration, but it is also conceivable that these sides form a trapezoidal shape.
According to another feature of the invention, the surface of the bottom that makes contact with the cam may have a slightly cylindrical shape. In this way, a larger contact surface is generated for contacting the cam.
Advantageously, the bottom is made in one piece with the sides and the skirt. However, a multi-piece structure involving a joining method, for example, is also conceivable.
For rigidifying the bottom, at least one stiffening rib can be provided on the inner surface of the bottom. Another possibility is to provide two opposing kidney-shaped stiffening ribs. If the cup tappet possesses a hydraulic clearance compensation element, an inner piston of the clearance compensation element can abut against the stiffening ribs, and this leads, at the same time, to the forming of an oil transfer passage from the tappet oil reservoir to the reservoir of the clearance compensation element.
It is proposed, particularly if the bottom has a rectangular shape, to provide an anti-rotation device in the skirt. This can be done using a means, known per se, for example, needle rollers, balls, wedges and the like.
According to a final proposition of the invention, the bottom has a general thickness of about 1.2 mm. This can be achieved by an optimization of rigidity using calculations based on finite element methods. Prior art cup tappets have a bottom thickness of about 1.8 mm.
As indicated above, the invention equally concerns both hydraulic and mechanical tappets.
The invention will now be described with reference to the appended drawing.